What does file optimization mean and how can I do it?
World Builders frequently talk about optimizing their worlds, sometimes the meaning of
this is not absolutely clear. The point is that smaller files download faster and this
allows people to see your creation quicker (like before they run out of patience).
The first trick that we employ is probably one you have
probably already seen. We compress the ASCII file with a utility called gzip. This
converts a human readable text format into a binary compressed format. All VRML plug-ins
know to gunzip these files automatically when they see a special code in
the compressed file's header. Typically we gzip the WRL file only, thought you can gzip
HTML files, it only makes sense when you have a very long page. It makes less sense to
gzip files which are already binary and already compressed such as GIF or JPG image files.
Gzip started out on UNIX operating systems but has been ported to other systems such as
windows. It is a free utility. You may find it a http://www.gzip.org
and it is already built into many applications such as Flux Studio© and VRMLpad©. Our friend
the Rev. Bob Crispen has added a windows style graphical user interface called WinGZ© that is free and easy to
use for single files. All your VRML files served from the Internet should be gzipped (an
exception may be for files that are 1 or 2KB, then it is more work to gunzip them that it
is to download them).
A second trick we often employ is to use a tool called
Chisel (by Trapezium). Chisel first checks your
files for correctness with a subprogram called Vorlon. This keeps you from publishing
files with structural or syntax errors. After Vorlon is done, you can then "thin
down" your files with several of the programs options (called chisels). Chisel should
be used with caution and I recommend making a backup copy of your file or saving each step
as a new file name as you go along. Chisel is sold as a stand-alone application, but
there is also a free web based version
The first Chisel is to Format the file by stripping out blanks at the
ends of lines and wrapping continuous fields of data onto one line where permissible.
Surprisingly, this simple step may knock 10% off the overall file size.
The next Chisel, Clean allows you to remove needless code that some
modeling applications create. It doesn't tend to have a large impact of file size, but
makes for cleaner code.
The next option is Condense. The selection that has the most impact is
Adjust Numeric Resolution. Some modeling tools output more precision than is typically
needed in VRML. A number such as 0.012345678 may be converted to 0.012 without affecting
the scene, but dramatically affecting download time. If 1.0 is a meter, then 0.1 is a
decimeter, 0.01 is a centimeter, and 0.001 is a millimeter. Typically we do not have a
need for sub-millimeter accuracy in a multi-user environment. This Chisel has the most
dramatic effect on large files with many Indexed Face Sets or other complicated geometry.
You should always use this Chisel on your final product. You can use the other Condense
options if Chisel indicates that you have issues in any of those areas.
Three decimal place precision is usually fine for our purposes. Many authoring
applications out put 5 to 7 significant digits.
1.0 = one meter
0.1 = one tenth of a meter (decimeter)
0.01 = one hundredth of a meter (centimeter)
0.001 = one thousandth of a meter (millimeter)
If you look at a meter stick, you will understand why real world scaled objects do not need
more precision than that. IF you are modeling molecules, galaxies or nuclear reactors;
then you may need greater or less precision, but for a couch....
Selecting create DEF/USE will allow Chisel to examine the code and if
it finds duplicated geometry (two identical IFS's) it will DEFine the first one and
replace the geometry with a USE statement (use the 1st geometry in this other place). This
makes the code more compact, but also may tend to make it less readable by humans. I
recommend this as a last step on a file that you are pretty certain you won't have to hand
edit again (or keep a copy of the original).
Remove unused DEF and Shorten DEF names will knock
2-3% off the file but will also make it much harder for a human to interpret the file by
hand editing later. I would use this with caution and when it is really needed.
I do not tend to use the Reorganize options unless I am doing
something special. The un-inline files can be handy if you are assembling many little
worlds through a "master" file. If I recall, it resolves problems of using the
same name for something different in several of the "imported" files.
The Reduce chisel can be handy to knock excess faces out of overly
complex geometry. There are better polygon reduction tools on the market, but these in
chisel do a fairly good job of reducing excess baggage from files. Use with caution, use
lightly, and make backups.
The Mutate options are interesting, but also just used for special
effects. The Pointcloud option is useful for reducing a bunch of planes (IFS) into a
series of points. The ElevationGrid to IFS can be handy when trying to use a complicated
"land surface" in an application that does not support Elevation Grids (e.g.
Flux Studio). This option may not be available in WebChisel. I use the IFS in Flux Studio
locating objects on the ground, then switch back to the Elevation Grid on my final product
(Elevation Grids are much smaller that IFSs).
Parallelgraphics will also format, and reduce numeric precision, and remove unused DEF
names when you use it to publish files.
The third and the best trick is, of course, hand coding
optimized files from scratch. People do not tend to type unneeded "fat" into
their files. Some tools employ scripts that may be more efficiently coded by hand
also, so even the scripts can be optimized for efficiency.
So, if you are not "hand-coding" or typing your worlds from scratch, it is
best to know that there are tools available which may be used that will help to improve
downloading and rendering time. Optimization is not required, but everyone will thank you